Titanium( IV ) and Zirconium( IV ) Sulfato Complexes Containing the Kläui Tripodal Ligand: Molecular Models of Sulfated Metal Oxide Surfaces

Treatment of titanyl sulfate in about 60 m M sulfuric acid with NaL OEt (L OEt − =[(η 5 ‐C 5 H 5 )Co{P(O)(OEt) 2 } 3 ] − ) afforded the μ‐sulfato complex [(L OEt Ti) 2 (μ‐O) 2 (μ‐SO 4 )] ( 2 ). In more concentrated sulfuric acid (>1  M ), the same reaction yielded the di‐μ‐sulfato complex [(L OEt Ti) 2 (μ‐O)(μ‐SO 4 ) 2 ] ( 3 ). Reaction of 2 with HOTf (OTf=triflate, CF 3 SO 3 ) gave the tris(triflato) complex [L OEt Ti(OTf) 3 ] ( 4 ), whereas treatment of 2 with Ag(OTf) in CH 2 Cl 2 afforded the sulfato‐capped trinuclear complex [{(L OEt ) 3 Ti 3 (μ‐O) 3 }(μ 3 ‐SO 4 ){Ag(OTf)}][OTf] ( 5 ), in which the Ag(OTf) moiety binds to a μ‐oxo group in the Ti 3 (μ‐O) 3 core. Reaction of 2 in H 2 O with Ba(NO 3 ) 2 afforded the tetranuclear complex (L OEt ) 4 Ti 4 (μ‐O) 6 ( 6 ). Treatment of 2 with [{Rh(cod)Cl} 2 ] (cod=1,5‐cyclooctadiene), [Re(CO) 5 Cl], and [Ru( t Bu 2 bpy)(PPh 3 ) 2 Cl 2 ] ( t Bu 2 bp y =4,4′‐di‐ tert ‐butyl‐2,2′‐dipyridyl) in the presence of Ag(OTf) afforded the heterometallic complexes [(L OEt ) 2 Ti 2 (O) 2 (SO 4 ){Rh(cod)} 2 ][OTf] 2 ( 7 ), [(L OEt ) 2 Ti(O) 2 (SO 4 ){Re(CO) 3 }][OTf] ( 8 ), and [{(L OEt ) 2 Ti 2 (μ‐O)}(μ 3 ‐SO 4 )(μ‐O) 2 {Ru(PPh 3 )( t Bu 2 bpy)}][OTf] 2 ( 9 ), respectively. Complex 9 is paramagnetic with a measured magnetic moment of about 2.4 μ B . Treatment of zirconyl nitrate with NaL OEt in 3.5  M sulfuric acid afforded [(L OEt ) 2 Zr(NO 3 )][L OEt Zr(SO 4 )(NO 3 )] ( 10 ). Reaction of ZrCl 4 in 1.8  M sulfuric acid with NaL OEt in the presence Na 2 SO 4 gave the μ‐sulfato‐bridged complex [L OEt Zr(SO 4 )(H 2 O)] 2 (μ‐SO 4 ) ( 11 ). Treatment of 11 with triflic acid afforded [(L OEt ) 2 Zr][OTf] 2 ( 12 ), whereas reaction of 11 with Ag(OTf) afforded a mixture of 12 and trinuclear [{L OEt Zr(SO 4 )(H 2 O)} 3 (μ 3 ‐SO 4 )][OTf] ( 13 ). The Zr IV triflato complex [L OEt Zr(OTf) 3 ] ( 14 ) was prepared by reaction of L OEt ZrF 3 with Me 3 SiOTf. Complexes 4 and 14 can catalyze the Diels–Alder reaction of 1,3‐cyclohexadiene with acrolein in good selectivity. Complexes 2 – 5 , 9 – 11 , and 13 have been characterized by X‐ray crystallography.